Graphene nanoribbons, graphene nanoplatelets and mixtures thereof and methods of synthesis

ABSTRACT

Provided herein are graphene nanoribbons with high structural uniformity and low levels of impurities and methods of synthesis thereof. Also provided herein are graphene nanoplatelets of superior structural uniformity and low levels of impurities and methods of synthesis thereof. Further provided herein are mixtures of graphene nanoribbons and graphene nanoplatelets of good structural uniformity and low levels of impurities and methods of synthesis thereof. The method includes, for example, the steps of depositing catalyst on a constantly moving substrate, forming carbon nanotubes on the substrate, separating carbon nanotubes from the substrate, collecting the carbon nanotubes from the surface where the substrate moves continuously and sequentially through the depositing, forming, separating and collecting steps. Further processing steps convert the synthesized carbon nanotubes to graphene nanoribbons, graphene nanoplatelets and mixtures thereof.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 (e) from UnitedStates Provisional Application Ser. No. 62/548,942 filed Aug. 22, 2017,U.S. Provisional Application Ser. No. 62/548,945 filed Aug. 22, 2017,U.S. Provisional Application Ser. No. 62/548,952 filed Aug. 22, 2017 andU.S. Provisional Application Ser. No. 62/548,955 filed Aug. 22, 2017 andis a divisional of Ser. No. 16/108,676, filed Aug. 21, 2018 which areall hereby incorporated by reference in their entirety.

FIELD

Provided herein are graphene nanoribbons with high structural uniformityand low levels of impurities and methods of synthesis thereof. Alsoprovided herein are graphene nanoplatelets of superior structuraluniformity and low levels of impurities and methods of synthesisthereof. Further provided herein are mixtures of graphene nanoribbonsand graphene nanoplatelets of good structural uniformity and low levelsof impurities and methods of synthesis thereof. The method includes, forexample, the steps of depositing catalyst on a constantly movingsubstrate, forming carbon nanotubes on the substrate, separating carbonnanotubes from the substrate, collecting the carbon nanotubes from thesurface where the substrate moves continuously and sequentially throughthe depositing, forming, separating and collecting steps. Furtherprocessing steps convert the synthesized carbon nanotubes to graphenenanoribbons, graphene nanoplatelets and mixtures thereof.

BACKGROUND

Graphene nanoribbons (GNRs) are a single or a few layers of thewell-known carbon allotrope graphitic carbon, which possessesexceptional electrical and physical properties which may lead toapplication in electronic devices, transistor fabrication and oiladditives. GNRs structurally have high aspect ratio with length beingmuch longer than the width or thickness.

Graphene nanoplatelets (GNPs) are similar to GNRs except that that thelength is in the micron or sub-micron range and hence GNPs lack the highaspect ratio of GNRs. GNPs also possess many of the useful properties ofcarbon nanotubes (CNTs) and GNRs.

GNRs have been prepared by CVD and from graphite using chemicalprocesses. Most typically GNRs were prepared from CNTs by chemicalunzipping and the quality of GNRs depends the purity of the CNT startingmaterial.

GNPs have been typically prepared from graphite by chemical exfoliation,thermal shock and shear, or in a plasma reactor. However, the abovemethods fail to provide GNRs and GNPs in high yield, good purity withgood control of width and length.

Recently, a number of methods have emerged which convert carbonnanotubes to GNRs in good yield and high purity (Hirsch, Angew Chem.Int. Ed. 2009, 48, 2694). More extreme conditions of some of the abovemethods used to prepare GNRs can result in the synthesis of GNPs fromGNRs. However, the purity and uniformity of carbon nanotubes and of theGNRs and GNPs produced from these CNTs is determined by the method ofmanufacture of the CNTs.

Current CNT manufacturing methods typically produce CNTs which includesignificant impurities such as, for example, metal catalysts andamorphous carbons. Purification steps are typically required aftersynthesis of CNTs, which are flow reactor methods to provide carbonnanotubes which are not contaminated with significant amounts of metalcatalysts and amorphous carbon. CNT purification steps require large andexpensive chemical plants which makes producing large quantities of CNTsof greater than 90% purity extremely costly. Furthermore, present CNTmanufacturing methods produce CNTs with low structural uniformity (i.e.,CNTs of variable lengths).

Accordingly, what is needed are new methods for providing high qualityand inexpensive GNRs and GNPs with high structural uniformity andpurity. These methods will involve preparing CNTs of high structuraluniformity and purity which then may be converted to GNRs and GNPs ofhigh structural uniformity and purity.

SUMMARY

The present invention satisfies these and other needs by providing, inone aspect, methods for synthesizing graphene nanoribbons. In someembodiments, the method includes the steps of depositing catalyst on aconstantly moving substrate, forming carbon nanotubes on the substrate,separating carbon nanotubes from the substrate, collecting the carbonnanotubes and converting the carbon nanotubes to graphene nanoribbonswherein the substrate moves sequentially through the depositing,forming, separating steps and collecting steps.

In another aspect, graphene nanoribbons of uniform length and greaterthan 95% purity are provided.

In still another aspect, methods for synthesizing graphene nanoplateletsare provided. In some embodiments, the method includes the steps ofdepositing catalyst on a constantly moving substrate, forming carbonnanotubes on the substrate, separating carbon nanotubes from thesubstrate, collecting the carbon nanotubes and converting the carbonnanotubes to graphene nanoplatelets wherein the substrate movessequentially through the depositing, forming, separating steps andcollecting steps.

In still another aspect, graphene nanoplatelets of uniform length andgreater than 95% purity are provided.

In still another aspect, methods for synthesizing a mixture of graphenenanoribbons and graphene nanoplatelets are provided. In someembodiments, the method includes the steps of depositing catalyst on aconstantly moving substrate, forming carbon nanotubes on the substrate,separating carbon nanotubes from the substrate, collecting the carbonnanotubes and converting the carbon nanotubes to a mixture of graphenenanoribbons and graphene nanoplatelets wherein the substrate movessequentially through the depositing, forming, separating steps andcollecting steps.

In still another aspect, a mixture of graphene nanoribbon and graphenenanoplatelets of uniform length and greater than 95% purity areprovided.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates an exemplary flowchart for synthesis of carbonnanotubes, which includes the steps of depositing catalyst on asubstrate; forming carbon nanotubes on a substrate; separating carbonnanotubes from the substrates; and collecting carbon nanotubes of highpurity and structural uniformity

FIG. 2 illustrates an exemplary flowchart for synthesis of carbonnanotubes, which includes the steps of forming carbon nanotubes on asubstrate; separating carbon nanotubes from the substrates; andcollecting carbon nanotubes of high purity and structural uniformity.

FIG. 3 illustrates an exemplary flowchart for continuous synthesis ofcarbon nanotubes, which includes the steps of continuously depositingcatalyst on a constantly moving substrate; forming CNTs on the movingsubstrate; separating CNTs from the moving substrate; and collectingcarbon nanotubes of high purity and structural uniformity.

FIG. 4 illustrates an exemplary flowchart for continuous synthesis ofcarbon nanotubes, which includes the steps of forming CNTs on the movingsubstrate containing metal substrate; separating CNTs from the movingsubstrate; and collecting carbon nanotubes of high purity and structuraluniformity.

FIG. 5 schematically illustrates a device for the continuous synthesisof carbon nanotubes, which includes various modules sequentiallydisposed such as a transport module for advancing the substrate throughthe modules; a catalyst module; a nanotube synthesis module; aseparation module; and a collection module.

FIG. 6 schematically illustrates a device with closed-loop feeding ofsubstrate for the continuous synthesis of carbon nanotubes whichincludes various modules sequentially disposed such as a transportmodule for advancing the substrate through the modules; a catalystmodule; a nanotube synthesis module; a separation module; and acollection module.

FIG. 7 schematically illustrates an exemplary separation module.

FIG. 8 schematically illustrates a horizontal view of a rectangularquartz chamber, that includes multiple substrates, which may be used inthe nanotube synthesis module.

FIG. 9 illustrates a perspective view of a rectangular quartz chamber,that includes multiple substrates, which may be used in the nanotubesynthesis module.

FIG. 10 illustrates TGA results which show greater than 99.4% purity forMWCNTs produced by the methods and apparatus described herein.

FIG. 11 illustrates Raman spectra which shows that MWCNTs produced bythe methods and apparatus described herein are highly crystalline whencompared to industrial grade samples.

FIG. 12 illustrates TGA results which show greater than 99% purity forgraphene nanoribbons produced by the methods described herein.

FIG. 13 illustrates Raman spectra which shows that graphene nanoribbonsproduced by the methods described herein are highly crystalline whencompared to industrial grade samples.

FIG. 14 illustrates an electron micrograph of high purity graphenenanoribbons.

FIG. 15 illustrates an electron micrograph of a mixture of high puritygraphene nanoribbons with graphene nanoplatelets.

FIG. 16 illustrates an electron micrograph of high purity graphenenanoplatelets.

FIG. 17 illustrates how increasing the concentration of graphene(Nadditive-G100) in base oil reduces the friction coefficient and scardiameter in the four ball testing parameter.

DETAILED DESCRIPTION Definitions

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as is commonly understood by one of ordinary skillin the art to which this invention belongs. If there is a plurality ofdefinitions for a term herein, those in this section prevail unlessstated otherwise.

As used herein “carbon nanotubes” refer to allotropes of carbon with acylindrical structure. Carbon nanotubes may have defects such asinclusion of C5 and/or C7 ring structures, such that the carbon nanotubeis not straight, may have contain coiled structures and may containrandomly distributed defected sites in the C—C bonding arrangement.Carbon nanotubes may contain one or more concentric cylindrical layers.The term “carbon nanotubes” as used herein includes single walled carbonnanotubes, double walled carbon nanotubes multiwalled carbon nanotubesalone in purified form or as mixture thereof. In some embodiment, thecarbon nanotubes are multi-walled. In other embodiments, the carbonnanotubes are single-walled. In still other embodiments, the carbonnanotubes are double-walled. In still other embodiments, the carbonnanotubes are a mixture of single-walled and multi-walled nanotubes. Instill other embodiments, the carbon nanotubes are a mixture ofsingle-walled and double-walled nanotubes. In still other embodiments,the carbon nanotubes are a mixture of double-walled and multi-wallednanotubes. In still other embodiments, the carbon nanotubes are amixture of single-walled, double-walled and multi-walled nanotubes.

As used herein “multi-walled carbon nanotubes” refer to carbon nanotubescomposed of multiple concentrically nested graphene sheets withinterlayer distances like graphite.

As used herein “double-walled carbon nanotubes” refer to carbonnanotubes with two concentrically nested graphene sheets

As used herein “single-walled carbon nanotubes” refer to carbonnanotubes with a single cylindrical graphene layer.

As used herein “vertically-aligned carbon nanotubes” refer to an arrayof carbon nanotubes deposited on a substrate wherein the structures ofcarbon nanotubes are physically aligned perpendicular to the substrate.

As used herein “catalysts” or “metal catalysts” refer to a metal or acombination of metals such as Fe, Ni, Co, Cu, Ag, Pt, Pd, Au, etc. thatare used in the breakdown of hydrocarbon gases and aid in the formationof carbon nanotubes by chemical vapor deposition process.

As used herein “chemical vapor deposition” refers to plasma-enhancedchemical vapor deposition, thermal chemical vapor deposition, alcoholcatalytic CVD, vapor phase growth, aerogel supported CVD and laseassisted CVD

As used herein “plasma-enhanced chemical vapor deposition” refers to theuse of plasma (e.g., glow discharge) to transform a hydrocarbon gasmixture into excited species which deposit carbon nanotubes on asurface.

As used herein “thermal chemical vapor deposition” refers to the thermaldecomposition of hydrocarbon vapor in the presence of a catalyst whichmay be used to deposit carbon nanotubes on a surface.

As used herein “physical vapor deposition” refers to vacuum depositionmethods used to deposit thin films by condensation of a vaporized ofdesired film material onto film materials and includes techniques suchas cathodic arc deposition, electron beam deposition, evaporativedeposition, pulsed laser deposition and sputter deposition.

As used herein “forming carbon nanotubes” refers to any vapor depositionprocess, including the chemical and physical vapor deposition methodsdescribed herein, for forming carbon nanotubes on a substrate in areaction chamber.

Carbon nanotubes are relatively new materials with exceptional physicalproperties, such as superior current carrying capacity, high thermalconductivity, good mechanical strength, and large surface area, whichare advantageous in a number of applications. Carbon nanotubes possessexceptional thermal conductivity with a value as high as 3000 W/mK whichis only lower than the thermal conductivity of diamond. Carbon nanotubesare mechanically strong, thermally stable above 400° C. underatmospheric conditions and have reversible mechanical flexibilityparticularly when vertically aligned. Accordingly, carbon nanotubes canmechanically conform to different surface morphologies because of thisintrinsic flexibility. Additionally, carbon nanotubes have a low thermalexpansion coefficient and retain flexibility in confined conditionsunder elevated temperatures.

Economically providing carbon nanotubes, in a controlled manner withpractical and simple integration and/or packaging is essential forimplementing many carbon nanotube technologies. Devices and methodswhich provide large quantities of carbon nanotubes of exceptional purityand uniform length are provided herein. The CNTs synthesized herein donot require costly post-synthesis purification.

Briefly the general feature of the method are as follows. First, a metalcatalyst is coated on the surface and the substrate is heated at hightemperature. Then catalyst is then coated on the surface of thesubstrate at high temperature to provide nanoparticles of catalyst onthe substrate, which serve as initiation site for CNT synthesis. CNTsare synthesized by supplying a carbon source to the catalyst.Accordingly, a mixture of carbon source and carrier gas is flowed into achamber which included heated substrate coated with catalyst to providesubstrate with attached CNTs. Finally, synthesized CNTs are extractedfrom the substrate and collected. Optionally, the substrate coated withcatalyst is regenerated.

In some embodiments, the catalyst is deposited on the substrate bysputtering, evaporation, dip coating, print screening, electrospray,spray pyrolysis or ink jet printing. The catalyst may be then chemicallyetched or thermally annealed to induce catalyst particle nucleation. Thechoice of catalyst can lead to preferential growth of single walled CNTsover multi-walled CNTs.

In some embodiments, the catalyst is deposited on a substrate byimmersing the substrate in a solution of the catalyst. In otherembodiments, the concentration of the catalyst solution in aqueous ororganic solvents water is between about 0.01% and about 20%. In stillother embodiments, the concentration of the catalyst solution in aqueousor organic solvents water is between about 0.1% and about 10%. In stillother embodiments, the concentration of the catalyst solution in aqueousor organic solvents water is between about 1% and about 5%.

The temperature of the chamber where CNTs are made should be atemperature lower than the melting temperature of substrate, lower thanthe decomposition temperate of carbon source and higher than thedecomposition temperature of the catalyst raw material. The temperaturerange for growing multi-walled carbon nanotubes is between about 600° C.to about 900° C., while the temperature range for growing single walledCNTs is between about 700° C. to about 1100° C.

In some embodiments, CNTs are formed by chemical vapor deposition on asubstrate containing metal catalysts for the growth of CNTs. It isimportant to note that continuous CNT formation on a constantly movingsubstrate allows the CNTs to have uniform lengths. Typical feedstocksinclude, but are not limited to, carbon monoxide, acetylene, alcohols,ethylene, methane, benzene, etc. Carrier gases are inert gases such asfor example, argon, helium, or nitrogen, while hydrogen is a typicalreducing gas. The composition of the gas mixture and duration ofsubstrate exposure regulates the length of synthesized CNTs. Othermethods known to those of skill in the art such as, for example, thephysical vapor deposition methods described, supra, the method ofNikolaev et al., Chemical Physics Letter, 1999, 105, 10249-10256 andnebulized spray pyrolysis (Rao et al., Chem. Eng. Sci. 59, 466, 2004)may be used in the methods and devices described herein. Conditions wellknown to those of skill in the art may be used to prepare carbonnanotubes using any of the methods above.

Referring now to FIG. 1, a method for synthesizing carbon nanotubes isprovided. The method may be performed in discrete steps, as illustratedin FIG. 1. Those of skill in the art will appreciate that anycombination of the steps can be performed continuously, if desired. Acatalyst is deposited on a substrate at 102, carbon nanotubes are formedon the substrate at 104, carbon nanotubes are separated from thesubstrate at 106 and the carbon nanotubes are collected at 108.

Referring now to FIG. 2, another method for synthesizing carbonnanotubes is provided. The method may be performed in discrete steps, asillustrated in FIG. 2. Those of skill in the art will appreciate thatany combination of the steps can be performed continuously, if desired.Carbon nanotubes are formed on a substrate, which already containscatalyst at 202, carbon nanotubes are separated from the substrate at204 and the carbon nanotubes are collected at 206.

Referring now to FIG. 3, another method for synthesizing carbonnanotubes is provided. The method is performed continuously. A catalystis continuously deposited on a moving substrate at 302, carbon nanotubesare continuously formed on the moving substrate at 304, carbon nanotubesare continuously separated from the substrate at 306 and the carbonnanotubes are continuously collected at 308. The substrate may be cycledthrough the steps described herein once or optionally, many times, suchas, for example, more than 50 time, more than 1,000 time or more than100,000 times.

Referring now to FIG. 4, another method for synthesizing carbonnanotubes is provided. The method is performed continuously asillustrated. Carbon nanotubes are continuously formed on the movingsubstrate which already contains catalyst at 402, carbon nanotubes arecontinuously separated from the substrate at 404 and the carbonnanotubes are continuously collected at 406. In some embodiments, thesubstrate is cycled through the deposition, forming and separating stepsmore than 50 times, more than 1,000 time or more than 100,0000 times.

Deposition of CNTs on a moving substrate provides CNTs that are of bothhigh purity and high length uniformity. Moreover, controlling processconditions enables the customization of CNT length. For example,variation of the rate of the moving substrate through the productionprocess modifies CNT length; faster rates though the CNT depositionmodule produces CNT of shorter length, while slower rates will produceCNT of longer length.

In some embodiments, the substrate is completely covered by metal foil.In these embodiments, the substrate may be any material stable toconditions of catalyst deposition and CNT synthesis. Many such materialare known to those of skill in the art and include, for example, carbonfibers, carbon foil, silicon, quartz, etc. In other embodiments, thesubstrate is a metal foil which can be continuously advanced through thevarious steps of the methods described herein.

In some embodiments, the thickness of the metal foil is greater than 10μM. In other embodiments, the thickness of the metal foil is betweenabout 10 μM and about 500 μM. In still other embodiments, the thicknessof the metal foil is between about 500 μM and about 2000 μM. In stillother embodiments, the thickness of the metal foil is between about 0.05μM and about 100 cm. In other embodiments, the thickness of the metalfoil is between about 0.05 μM and about 100 cm. In other embodiments,the thickness of the metal foil is between about 0.05 mm and about 5 mm.In still other embodiments, the thickness of the metal foil is betweenabout 0.1 mm and about 2.5 mm. In still other embodiments, the thicknessof the metal foil is between about 0.5 mm and about 1.5 mm. In stillother embodiments, the thickness of the metal foil is between about 1 mmand about 5 mm. In still other embodiments, the thickness of the metalfoil is between about 0.05 mm and about 1 mm. In still otherembodiments, the thickness of the metal foil is between about 0.05 mmand about 0.5 mm. In still other embodiments, the thickness of the metalfoil is between about 0.5 mm and about 1 mm. In still other embodiments,the thickness of the metal foil is between about 1 mm and about 2.5 mm.In still other embodiments, the thickness of the metal foil is betweenabout 2.5 mm and about 5 mm. In still other embodiments, the thicknessof the metal foil is between about 100 μM and about 5 mm. In still otherembodiments, the thickness of the metal foil is between about 10 μM andabout 5 mm. In still other embodiments, the thickness of the metal foilis greater than 100 μM. In still other embodiments, the thickness of themetal foil is less than 100 μM.

In some embodiments, the metal foil includes iron, nickel, aluminum,cobalt, copper, chromium, gold, silver, platinum, palladium orcombinations thereof. In other embodiments, the metal foil includesiron, nickel, cobalt, copper, gold or combinations thereof. In someembodiments, the metal foil may be coated with organometallocenes, suchas, for example, ferrocene, cobaltocene or nickelocene.

In some embodiments, the metal foil is an alloy of two or more of iron,nickel, cobalt, copper, chromium, aluminum, gold or combinationsthereof. In other embodiments, the metal foil is an alloy of two or moreof iron, nickel, cobalt, copper, gold or combinations thereof.

In some embodiments, the metal foil is high temperature metal alloy. Inother embodiments, the metal foil is stainless steel. In still otherembodiments, the metal foil is a high temperature metal alloy on which acatalyst is deposited for growing carbon nanotubes. In still otherembodiments, the metal foil is stainless steel on which a catalyst isdeposited for growing carbon nanotubes.

In some embodiments, the metal foil is a metal or combination of metalswhich are thermally stable at greater than 400° C. In other embodiments,the metal foil is a metal or combination of metals which are thermallystable at greater than 500° C., greater than 600° C., greater than 700°C. or greater than 1000° C. In some of the above embodiments, thecombination of metals is stainless steel.

In some embodiments, the metal foil has a thickness of less than about100 μM and a surface root mean square roughness of less than about 250nm. In some embodiments, the metal foil has a thickness of greater thanabout 100 μM and a surface root mean square roughness of less than about250 nm. In still other embodiments, the metal foil has a thickness ofless than about 100 μM and a surface root mean square roughness of lessthan about 250 nm and includes iron, nickel, cobalt, copper, gold orcombinations thereof. In still other embodiments, the metal foil has athickness of greater than about 100 μM and a surface root mean squareroughness of less than about 250 nm and includes iron, nickel, cobalt,copper, gold or combinations thereof. In still other embodiments, themetal foil has a thickness of less than about 100 μM and a surface rootmean square roughness of less than about 250 nm and includes a catalystfilm. In still other embodiments, the metal foil has a thickness ofgreater than about 100 μM and a surface root mean square roughness ofless than about 250 nm and includes a catalyst film. In some of theabove embodiments, the root mean square roughness is less than about 100nm.

In some embodiments, the substrate continuously advances through thesteps of the above methods at a rate greater than 0.1 cm/minute. Inother embodiments, the substrate continuously advances through the stepsof the above methods at a rate greater than 0.05 cm/minute. In sillother embodiments, the substrate continuously advances through the stepsof the above methods at a rate greater than 0.01 cm/minute. In stillother embodiments, the substrate is cycled through the deposition,forming, separating and collecting steps more than 10 times 50 times,more than 1,000 time or more than 100,0000 times.

In some embodiments, the substrate is wider than about 1 cm. In otherembodiments, the substrate has a length greater than 1 m, 10 m, 100 m,1,000 m or 10,000 m. In some of these embodiments, the substrate is ametal foil.

In some embodiments, carbon nanotubes are formed on all sides of thesubstrate. In other embodiments, carbon nanotubes are formed on bothsides of the metal foil.

In some embodiments, the concentration of catalyst deposited on thesubstrate is between about 0.001% and about 25%. In other embodiments,the concentration of catalyst deposited on the substrate is betweenabout 0.1% and about 1%. In still other embodiments, the concentrationof catalyst deposited on the substrate is between about 0.5% and about20%.

In some embodiments, the concentration of carbon nanotube on thesubstrate is between about 1 nanotube per μM and about 50 nanotubes perμM. In other embodiments, the concentration of carbon nanotube on thesubstrate is between about 10 nanotubes per μM and about 500 nanotubesper μM.

In some embodiments, the CNTs are separated from the substrate bymechanical removal of the CNTs from the surface of the substrate. Inother embodiments, separation of CNTs from the substrate involvesremoving the CNTs from the surface of the substrate with a mechanicaltool (e.g., a blade, an abrasive surface, etc.) thus yielding highpurity CNTs with little or no metal impurities, which do not require anyadditional purification. In still other embodiments, separation of CNTsfrom the substrate involves chemical methods that disrupt adhesion ofCNTs to the substrate. In yet other embodiments, ultrasonicationdisrupts adhesion of CNTs to the substrate. In still other embodiments,pressurized gas flow disrupts adhesion of CNTs to the substrate. Thecombination of depositing CNTs on a substrate and separating CNTs fromthe substrate renders CNT products of uniform length free of catalystand amorphous carbon impurities.

The CNTs can be collected in or on any convenient object, such as forexample, an open vessel, a wire mesh screen, a solid surface, afiltration device, etc. The choice of collection device will becorrelated with the method used to disrupt adhesion of CNTs to thesubstrate.

In some embodiments, the carbon nanotubes are randomly aligned. In otherembodiments, the carbon nanotubes are vertically aligned. In still otherembodiments, the uniform length is on average about 50 μM, about 100 μM,about 150 μM or about 200 μM. In still other embodiments, the uniformlength can range from 50 μM to 2 cm. In general, the uniform length isabout +/−10% of the stated length. Accordingly, a sample with a uniformlength of about 100 μM will include nanotubes of length between 90 μMand 110 μM. In still other embodiments, carbon nanotubes are verticallyaligned and are of uniform length.

In some embodiments, the density of the carbon nanotubes is betweenabout 2 mg/cm2 and about 1 mg/cm2. In other embodiments, the density ofthe carbon nanotubes between about 2 mg/cm2 and about 0.2 mg/cm2.

In some embodiments, vertically aligned carbon nanotubes have a thermalconductivity of greater than about 50 W/mK. In other embodiments,vertically aligned carbon nanotubes have a thermal conductivity ofgreater than about 70 W/mK.

In some embodiments, the thickness of the vertically aligned carbonnanotubes is between than about 100 μm and about 500 μm. In otherembodiments, the thickness of the vertically aligned carbon nanotubes isless than about 100 μm.

In some embodiments, the carbon nanotubes are of greater than 90%, 95%,99%, 99.5% or 99.9% purity. In other embodiments, the carbon nanotubesare of greater than 90%, 95%, 99%, 99.5% or 99.9% purity and are ofuniform length of about 10 μM, about 20 μM, about 50 μM, about 100 μM,about 150 μM or about 200 μM. In still other embodiments, the carbonnanotubes are vertically aligned, of greater than 90%, 95%, 99%, 99.5%or 99.9% purity and are of uniform length of about 50 μM, about 100 μM,about 150 μM or about 200 μM.

In some embodiments, the tensile strength of the carbon nanotubes isbetween about 11 GPa and about 63 GPa. In other embodiments, the tensilestrength of the carbon nanotubes is between about 20 GPa and about 63GPa. In still other embodiments, the tensile strength of the carbonnanotubes is between about 30 GPa and about 63 GPa. In still otherembodiments, the tensile strength of the carbon nanotubes is betweenabout 40 GPa and about 63 GPa. In still other embodiments, the tensilestrength of the carbon nanotubes is between about 50 GPa and about 63GPa. In still other embodiments, the tensile strength of the carbonnanotubes is between about 20 GPa and about 45 GPa.

In some embodiments, the elastic modulus of the carbon nanotubes isbetween about 1.3 TPa and about 5 TPa. In other embodiments, the elasticmodulus of the carbon nanotubes is between about 1.7 TPa and about 2.5TPa. In still other embodiments, the elastic modulus of the carbonnanotubes is between about 2.7 TPa and about 3.8 TPa.

Referring now to FIG. 5, a device for continuously synthesizing CNTs isprovided. Transport module includes drums 501A and 501B, which areconnected by substrate 506. Substrate 506 continuously moves from drum501A through catalyst module 502, nanotube synthesis module 503 andseparation module 504 to drum 501B. Note that naïve substrate 506A, ismodified by catalyst module 502 to provide substrate 506B which containscatalyst. In some embodiments, catalyst module 502 is a solution ofcatalyst in which substrate 506A is immersed. Carbon nanotubes arecontinuously formed on substrate 506B during transit through nanotubesynthesis module 503 to yield substrate 506C, which includes carbonnanotubes. In some embodiments, nanotube synthesis module 503 is a CVDchamber. Substrate 506C is continuously processed by separation module504 and stripped of attached carbon nanotubes to yield substrate 506A,which is then collected by drum 501B. In some embodiments, separationmodule 504 includes a blade which mechanically shears the newly formedCNTs from substrate 506C. Note that carbon nanotubes removed fromsubstrate 506C are continuously collected by process 506D at collectionmodule 505. In some embodiments, collection module 505 is simply anempty vessel situated appropriately to collect the CNTs separated fromthe substrate surface by separation module 504. In the above embodiment,substrate 506 is not recycled during the production run.

Referring now to FIG. 6, another device for continuously synthesizingCNTs is schematically illustrated. Transport module includes drums 601Aand 601B, which are connected by substrate 606. Substrate 606continuously moves from drum 601A through catalyst module 602, nanotubesynthesis module 603 and separation module 604 to drum 601B. Note thatnaïve substrate 606A, is modified by catalyst module 602 to providesubstrate 606B which contains catalyst. In some embodiments, catalystmodule 502 is a solution of catalyst in which substrate 606A isimmersed. Carbon nanotubes are continuously formed on substrate 606Bduring transit through nanotube synthesis module 603 to yield substrate506C. In some embodiments, nanotube synthesis module 603 is a CVDchamber. Substrate 606C is continuously processed by separation module604 and stripped of attached carbon nanotubes to yield substrate 606A,which is then collected by drum 601B. In some embodiments, separationmodule 604 includes a blade which mechanically shears the newly formedCNTs from substrate 606C. Note that carbon nanotubes removed fromsubstrate 606C are continuously collected by process 606D at collectionmodule 605. In some embodiments, collection module 605 is simply anempty vessel situated appropriately to collect the CNTs separated fromthe substrate surface by separation module 604. In the above embodiment,the substrate is recycled through the production run at least once.

Although many of the above embodiments have been described assynthesizing nanotubes continuously, those of skill in the art willappreciate that the methods and devices described herein may bepracticed discontinuously.

FIG. 7 schematically illustrates an exemplary separation module. Drum704 advances substrate 701, which has been processed by catalyst module(not shown) and carbon nanotube deposition module (not shown) and whichis covered with carbon nanotubes to tool 700, which removes carbonnanotubes 702 to provide substrate 703 devoid of carbon nanotubes. Insome embodiments, tool 700 is a cutting blade. The substrate 703 iscollected by drum 705. Carbon nanotubes 702 are collected in container706. Substrate 701, as illustrated, is coated on only one side withcarbon nanotubes. Those of skill in the art will appreciate thatnanotubes can be grown on both sides of the substrate and that asubstrate with both sides coated can be processed in a manner analogousto that described above.

FIG. 8 illustrates a horizontal view of an exemplary rectangular quartzchamber 800, which may be used in the nanotube synthesis module thatincludes multiple substrates 801, which contain catalyst. FIG. 9illustrates a perspective view of an exemplary rectangular quartzchamber 900, which may be used in the nanotube synthesis module thatincludes multiple substrates 901, which contain catalyst. The quartzchamber includes shower heads (not shown) for carrier gases and carbonfeedstocks and may be heated at temperatures sufficient to form CNTs. Insome embodiment, the chamber has inner chamber thickness of greater than0.2 inch. In other embodiments, more than substrate is processed by thechamber simultaneously.

CNTs can be characterized by a multitude of techniques, including, forexample, Raman, spectroscopy, UV, visible, near infrared spectroscopy,florescence and X-ray photoelectron spectroscopy, thermogravimetricanalysis, atomic force microscopy, scanning tunneling, microcopy,scanning electron microscopy and tunneling electron microscopy. Acombination of many, if not all of the above are sufficient to fullycharacterize carbon nanotubes.

In general, graphene nanoribbons can be prepared from CNTs byconventional methods known in the art which include but are not limitedto acid oxidation (e.g., Kosynkin et al., Nature, 2009, 458, 872;Higginbotham et al., ACS Nano, 210, 4, 2596; Cataldo et al., Carbon,2010, 48, 2596; Kang et al., J. Mater. Chem., 2012, 22, 16283; andDhakate et al., Carbon 2011, 49, 4170), plasma etching (e.g, Jiao etal., Nature, 2009, 458, 877; Mohammadi et al., Carbon, 2013, 52, 451;and Jiao et al., Nano Res 2010, 3, 387), ionic intercalation, (e.g.,Cano-Marques et al., Nano Lett. 2010, 10, 366), metal particle catalysis(e.g., Elias et al., Nano Lett. Nano Lett., 2010, 10, 366; and Parasharet. al., Nanaoscale, 2011, 3, 3876), hydrogenation (Talyzin et al., ACSNano, 2011, 5, 5132) and sonochemistry (Xie et al., J. Am. Chem. Soc.2011, DOI: 10.1021/ja203860). Any of the above methods may be used toprepare graphene nanoribbons from the CNTs described herein. Referringnow to FIG. 14, an electron micrograph herein illustrates the highpurity of the graphene nanoribbons produced by the methods describedherein.

Graphene nanoplatelets may be produced from CNTs by further oxidation ofGNRs produced from CNTs. Accordingly, those of skill in the art willunderstand that production of GNPs as described herein proceeds throughthe intermediacy of GNRs. For example, GNPs can be made from GNRs byacid oxidation at higher temperatures and/or longer reaction times orplasma etching at higher temperature or under more forcing conditions.Referring now to FIG. 16, an electron micrograph herein illustrates thehigh purity of the graphene nanoplatelets produced by the methodsdescribed herein.

Mixtures of graphene nanoplatelets and graphene nanoribbons are alsoprovided herein. Such mixture may be provided by incomplete oxidation ofgraphene nanoribbons to graphene nanoplatelets or by mixing puregraphene nanoribbons with graphene nanoplatelets. Referring now to FIG.15, an electron micrograph herein illustrates the high purity of amixture of graphene nanoribbons and graphene nanoplatelets produced bythe methods described herein. All mixtures of graphene nanoribbons andgraphene nanoplatelets are envisioned herein. Accordingly, the mixturemay range between about 0.001% graphene nanoribbons and about 99.999%graphene nanoplatelets to between about 99.999% graphene nanoribbons andabout 0.0001% graphene nanoplatelets.

In some embodiments, a mixture of 1% graphene nanoribbons and about 99%graphene nanoplatelets is provided. In other embodiments, a mixture of5% graphene nanoribbons and about 95% graphene nanoplatelets isprovided. In still other embodiments, a mixture of 10% graphenenanoribbons and about 90% graphene nanoplatelets is provided. In stillother embodiments, a mixture of 20% graphene nanoribbons and about 80%graphene nanoplatelets is provided. In still other embodiments, amixture of 30% graphene nanoribbons and about 70% graphene nanoplateletsis provided. In still other embodiments, a mixture of 40% graphenenanoribbons and about 60% graphene nanoplatelets is provided. In stillother embodiments, a mixture of 50% graphene nanoribbons and about 50%graphene nanoplatelets is provided. In still other embodiments, amixture of 60% graphene nanoribbons and about 40% graphene nanoplateletsis provided. In still other embodiments, a mixture of 70% graphenenanoribbons and about 30% graphene nanoplatelets is provided. In stillother embodiments, a mixture of 80% graphene nanoribbons and about 20%graphene nanoplatelets is provided. In still other embodiments, amixture of 90% graphene nanoribbons and about 10% graphene nanoplateletsis provided. In still other embodiments, a mixture of 95% graphenenanoribbons and about 5% graphene nanoplatelets is provided. In stillother embodiments, a mixture of 99% graphene nanoribbons and about 1%graphene nanoplatelets is provided.

In some embodiments, the uniform length of the graphene nanoribbons ison average about 10 μM, about 20 μM, about 50 μM, about 100 μM, about150 μM or about 200 μM. In other embodiments, the uniform length canrange from 50 μM to 2 cm. In general, the uniform length is about +/−10%of the stated length. Accordingly, a sample with a uniform length ofabout 100 μM will include GNRs of length between 90 μM and 110 μM.

In some embodiments, the graphene nanoribbons are made from carbonnanotubes of uniform length of which is on average about 10 μM, about 20μM, about 50 μM, about 100 μM, about 150 μM or about 200 μM.

In some embodiments, the graphene nanoribbons are of greater than 90%,95%, 99%, 99.5% or 99.9% purity. In other embodiments, graphenenanoribbons are of greater than 90%, 95%, 99%, 99.5% or 99.9% purity andare of uniform length of about 10 μM, about 20 μM, about 50 μM, about100 μM, about 150 μM or about 200 μM.

In some embodiments, the uniform length of the graphene nanoplatelets ison average about about 10 μM, about 20 μM, 50 μM, about 100 μM, about150 μM or about 200 μM. In other embodiments, the uniform length canrange from 50 μM to 2 cm. In general, the uniform length is about +/−10%of the stated length. Accordingly, a sample with a uniform length ofabout 100 μM will include nanotubes of length between 90 μM and 110 μM.

In some embodiments, the graphene nanoplatelets are made from carbonnanotubes of uniform length of which is on average about 10 μM, about 20μM, about 50 μM, about 100 μM, about 150 μM or about 200 μM.

In some embodiments, the graphene nanoplatelets are of greater than 90%,95%, 99%, 99.5% or 99.9% purity. In other embodiments, graphenenanoribbons are of greater than 90%, 95%, 99%, 99.5% or 99.9% purity andare of uniform length of about 50 μM, about 100 μM, about 150 μM orabout 200 μM.

In some embodiments, a mixture of 1% graphene nanoribbons and about 99%graphene nanoplatelets is provided. In other embodiments, a mixture of5% graphene nanoribbons and about 95% graphene nanoplatelets isprovided. In still other embodiments, a mixture of 10% graphenenanoribbons and about 90% graphene nanoplatelets is provided. In stillother embodiments, a mixture of 20% graphene nanoribbons and about 80%graphene nanoplatelets is provided. In still other embodiments, amixture of 30% graphene nanoribbons and about 70% graphene nanoplateletsis provided. In still other embodiments, a mixture of 40% graphenenanoribbons and about 60% graphene nanoplatelets is provided. In stillother embodiments, a mixture of 50% graphene nanoribbons and about 50%graphene nanoplatelets is provided. In still other embodiments, amixture of 60% graphene nanoribbons and about 40% graphene nanoplateletsis provided. In still other embodiments, a mixture of 70% graphenenanoribbons and about 30% graphene nanoplatelets is provided. In stillother embodiments, a mixture of 80% graphene nanoribbons and about 20%graphene nanoplatelets is provided. In still other embodiments, amixture of 90% graphene nanoribbons and about 10% graphene nanoplateletsis provided. In still other embodiments, a mixture of 95% graphenenanoribbons and about 5% graphene nanoplatelets is provided. In stillother embodiments, a mixture of 99% graphene nanoribbons and about 1%graphene nanoplatelets is provided.

The skilled artisan will appreciate that the graphene nanoribbons andthe graphene nanoplatelets in the mixture can have the same purityand/or uniform lengths described above for pure graphene nanoribbons andgraphene nanoplatelets. In some embodiments, the mixtures of graphenenanoribbons and graphene have the same purity and the same uniformlength. In other embodiments, the mixtures of graphene nanoribbons andgraphene have different purity and the same uniform length. In stillother embodiments, the mixtures of graphene nanoribbons and graphenehave the same purity and different length.

The purity and structural uniformity, such as, for example, length andwidth of graphene nanoribbons and graphene nanoplatelets or mixturesthereof, is essential for manufacturing regularity to consistentlyprovide high performance and superior quality graphene nanoribbon,graphene nanoplatelet or mixtures thereof containing products. Someexamples of uses of graphene nanoribbons, graphene nanoplatelets ormixtures thereof are as fillers in polymeric composites, protectivecoatings on metal surfaces, (reduces wear of metal surfaces, leads toreduction in coefficient of friction) lubricant additives, contrastimaging agents, nanoelectronics, transistor material, transparentconductive films, sensor, electrode material for batteries includingLI-ion batteries for EVs, and supercapacitors.

Graphene nanoribbons, graphene nanoplatelets or mixtures thereof areuseful oil and lubricant additives. In some embodiments, graphenenanoribbons, graphene nanoplatelets or mixtures thereof, which aregreater than 90%, 95%, 99%, 99.5% or 99.9% purity form a stablesuspension when added to a lubricant or an oil. In other embodiments,graphene nanoribbons, graphene nanoplatelets or mixtures thereof, whichare greater than 90%, 95%, 99%, 99.5% or 99.9% purity and are of uniformlength of about 50 μM, about 100 μM, about 150 μM or about 200 μM form astable suspension when added to a lubricant or oil.

Graphene nanoribbons, graphene nanoplatelets or mixtures thereof reducethe coefficient of friction to less than 0.07 when used as lubricant oroil additives. In some embodiments, graphene nanoribbons, graphenenanoplatelets or mixtures thereof of greater than 90%, 95%, 99%, 99.5%or 99.9% purity reduce the coefficient of friction in lubricants or oilsto less than 0.07. In other embodiments, graphene nanoribbons, graphenenanoplatelets or mixtures thereof, which are greater than 90%, 95%, 99%,99.5% or 99.9% purity and are of uniform length of about 50 μM, about100 μM, about 150 μM or about 200 μM purity reduce the coefficient offriction in lubricants or oil to less than 0.07.

Graphene nanoribbons, graphene nanoplatelets or mixtures thereof reducethe coefficient of friction to less than 0.05 when used as lubricant oroil additives. In some embodiments, graphene nanoribbons, graphenenanoplatelets or mixtures thereof of greater than 90%, 95%, 99%, 99.5%or 99.9% purity reduce the coefficient of friction in lubricants andoils to less than 0.07. In other embodiments, graphene nanoribbons,graphene nanoplatelets or mixtures thereof, which are greater than 90%,95%, 99%, 99.5% or 99.9% purity and are of uniform length of about 50μM, about 100 μM, about 150 μM or about 200 μM purity reduce thecoefficient of friction in lubricants and oils to less than 0.05.

Graphene nanoribbons, graphene nanoplatelets or mixtures thereof whenused as a lubricant or oil additive improve fuel consumption. In someembodiments, graphene nanoribbons, graphene nanoplatelets or mixturesthereof of greater than 90%, 95%, 99%, 99.5% or 99.9% purity when usedas a lubricant or oil additive improve fuel consumption by greater than3%, greater than 5%, greater than 10% or greater than 20%. In otherembodiments, graphene nanoribbons, graphene nanoplatelets or mixturesthereof, which are greater than 90%, 95%, 99%, 99.5% or 99.9% purity andare of uniform length of about 50 μM, about 100 μM, about 150 μM orabout 200 μM purity when used as a lubricant or oil additive improvefuel consumption by greater than 3%, greater than 5%, greater than 10%or greater than 20%.

Graphene nanoribbons, graphene nanoplatelets or mixtures thereof whenused as a lubricant or oil additive reduce smoke and/or NOx emission. Insome embodiments, graphene nanoribbons, graphene nanoplatelets ormixtures thereof of greater than 90%, 95%, 99%, 99.5% or 99.9% puritywhen used as a lubricant or oil additive reduce smoke and/or NOxemission. In other embodiments, graphene nanoribbons, graphenenanoplatelets or mixtures thereof, which are greater than 90%, 95%, 99%,99.5% or 99.9% purity and are of uniform length of about 50 μM, about100 μM, about 150 μM or about 200 μM purity when used as a lubricant oroil additive reduce smoke and/or NOx emission.

Lubricants or oils which include graphene additives reduce friction,increase mileage, extend engine life, increase horsepower andacceleration, reduce engine noise and increase fuel efficiency. Withoutwishing to bound by theory the lubricant, which includes graphenenanoribbons, graphene nanoplatelets or mixtures thereof coats all movingcomponents with a protective film of fluid. The extreme mechanicalstrength of graphene additives is of great significance in protectingmoving parts from excessive wear.

In some embodiments, graphene nanoribbons, graphene nanoplatelets ormixtures thereof reduce engine wear when used as a lubricant or oiladditive. In other embodiments, graphene nanoribbons, graphenenanoplatelets or mixtures thereof improve engine lifetime when used as alubricant or oil additive. Without wishing to bound by theory graphenenanoribbons, graphene nanoplatelets or mixtures thereof when used as alubricant or oil additive may form a protective coating on enginecomponents which reduces engine wear and/or increases engine lifetime.In some embodiments, the graphene nanoribbons, graphene nanoplatelets ormixtures thereof of greater than 90%, 95%, 99%, 99.5% or 99.9% puritywhen used as a lubricant or oil additive reduce engine wear and/orincreases engine lifetime. In other embodiments, graphene nanoribbons,graphene nanoplatelets or mixtures thereof, which are greater than 90%,95%, 99%, 99.5% or 99.9% purity and are of uniform length of about 50μM, about 100 μM, about 150 μM or about 200 μM purity when used as anadditive in lubricants or oils reduces engine wear and/or increasesengine lifetime.

Finally, it should be noted that there are alternative ways ofimplementing the present invention. Accordingly, the present embodimentsare to be considered as illustrative and not restrictive, and theinvention is not to be limited to the details given herein but may bemodified within the scope and equivalents of the appended claims.

All publications and patents cited herein are incorporated by referencein their entirety.

The following examples are provided for illustrative purposes only andare not intended to limit the scope of the invention.

Example 1: Thermogravimetric Analysis of Multiwalled CNTs

The carbon purity and thermal stability of CNTs were tested using aThermogravimetric Analyzer (TGA), TA instruments, Q500. The samples wereheated under air atmosphere (Praxair AI NDK) from temperature to 900° C.at a rate of 10° C./min and held at 900° C. for 10 minutes beforecooling. Carbon purity is defined as (weight of all carbonaceousmaterial)/(weight of all carbonaceous materials+weight of catalyst). Theinflection point is the temperature at which thermal degradation reachesits maximum value. The onset point is the temperature at which about 10%of the material degrades owing to high temperature. FIG. 10 illustratesthermal stability data for multi-walled carbon nanotubes made by themethods and devices described herein. The multi-walled carbon nanotubesmade herein have an inside diameter of about 5 nm with between 5-8 wallswith a customizable length of between 10 μM and 200 μM. In the regionbelow 400° C. is where amorphous carbon and carbonaceous materials withpoor thermal resistance were degraded. As can be seen from the graphthere is almost no amorphous carbon and carbonaceous materials in themulti-walled carbon nanotubes made by the methods and devices describedherein. The inflection point is 721° C., the onset point is 644° C. andthe carbon purity is greater than 99.4%. In contrast, in a commerciallyavailable CNT (not shown) the inflection point is 643° C., the onsetpoint is 583° C. and the carbon purity is 90%.

Example 2: Raman Analysis of Multiwalled CNTs

10 mg of CNTs were suspended in about 100 mL of methanol to form ablackish solution. The resulting suspension was then sonicated for about10 minutes to uniformly disperse CNTs in the suspension since a thinlayer of CNTs is required for Raman spectra. The suspension was thenspread over Si substrate to form a thin layer. The coated Si substratewas then placed in an oven for 10 minutes at 130° C. to vaporize thedispersing agent from the sample. Raman spectra were then recorded witha Thermos Nicolet Dispersive XR Raman Microscope with a laser radiationof 532 nm, integration of 50 s, 10× objective and a laser of 24 mW. Theratio of D and G band intensities is often used as a diagnostic tool toverify the structural perfection of CNTs.

FIG. 11 illustrates Raman spectra of multi-walled carbon nanotubes madeby the methods and devices described herein (solid line) andcommercially available CNTs (dashed line). The ID/IG and the IG/IG′ratio of the multi-walled carbon nanotubes made by the methods anddevices described herein are 0.76 and 0.44 respectively, while the sameratios for commercially available CNTs are 1.27 and 0.4, respectively.The above demonstrates, the greater crystallinity of the multi-walledcarbon nanotubes made by the methods and devices described herein overthose produced by other methods and is in accord with the thermalstability data.

Example 3: Thermogravimetric Analysis of Multiwalled GNRs

The carbon purity and thermal stability of CNTs were tested using aThermogravimetric Analyzer (TGA), TA instruments, Q500. The samples wereheated under air atmosphere (Praxair AI NDK) from temperature to 900° C.at a rate of 10° C./min and held at 900° C. for 10 minutes beforecooling. Carbon purity is defined as (weight of all carbonaceousmaterial)/(weight of all carbonaceous materials+weight of catalyst). Theinflection point is the temperature at which thermal degradation reachesits maximum value. The onset point is the temperature at which about 10%of the material degrades owing to high temperature. FIG. 12 illustratesthermal stability data for GNRs made by the methods described herein.The GNRs made have a customizable length of between 10 μM and 200 μM. Inthe region below 400° C. is where amorphous carbon and carbonaceousmaterials with poor thermal resistance were degraded. As can be seenfrom the graph there is almost no amorphous carbon and carbonaceousmaterials in the GNRs made by the methods and devices described herein.The inflection point is 690° C. and the carbon purity is greater than99.4%.

Example 4: Raman Analysis of GNRs

10 mg of CNTs were suspended in about 100 mL of methanol to form ablackish solution. The resulting suspension was then sonicated for about10 minutes to uniformly disperse CNTs in the suspension since a thinlayer of CNTs is required for Raman spectra. The suspension was thenspread over Si substrate to form a thin layer. The coated Si substratewas then placed in an oven for 10 minutes at 130° C. to vaporize thedispersing agent from the sample. Raman spectra were then recorded witha Thermos Nicolet Dispersive XR Raman Microscope with a laser radiationof 532 nm, integration of 50 s, 10× objective and a laser of 24 mW. Theratio of D and G band intensities is often used as a diagnostic tool toverify the structural perfection of CNTs.

FIG. 13 illustrates Raman spectra of GNRs made by the methods describedherein (solid line). The I2D/IG and ID/IG of the GNRs made by themethods described herein are 0.6 and 0.75 respectively, whichdemonstrates the standard graphene signature and illustrates minimaldefects from the chemical unzipping process.

Example 5: Frictional Coefficient and Scar Test Results for GrapheneBased Engine Oil Nanofluids

A standard four ball testing machine was used to measure the effect ofincreasing concentration of Nadditive-G100 (about 70% nanoplatelets andabout 30% graphene nanoribbons) with purity of greater than 99% in motoroil SN 5W-40. The tester was operated with one steel ball under loadrotating against three steel balls held stationary in a cradle. Therotating speed was 1200 RPM at 75° C. under a constant load of 40 Kg/Ffor a duration of 60 minutes. The results are show in FIG. 17, whichdemonstrates that increasing amounts of N-additive-G100 in motor oilsignificantly reduces the coefficient of friction and scar diameter.

Example 6: Vehicle Testing of Graphene Based Engine Oil Nanofluids

Fuel consumption Fuel consumption for graphene oil (25 for commercialmg/L of N-G100) in Efficiency Vehicle (Year) oil commercial oil increase(%) Honda Pilot 23.45 mpg 25.82 mpg 10.1 (2014) VW Golf 20.67 mpg 22.63mpg 9.5 Mitsubishi 25.78 mpg 28 mpg 8.6 Lancer

The above results show that graphene oil additives increase fuelconsumption in tested vehicles by between about 10% to about 20%.

What is claimed is:
 1. A method for synthesizing graphene nanoribbonscomprising: continuously depositing catalyst on a constantly movingsubstrate; forming carbon nanotubes on the substrate; separating carbonnanotubes from the substrate; collecting carbon nanotubes; andconverting the carbon nanotubes to graphene nanoribbons; wherein thesubstrate moves sequentially through the depositing, forming,separating, collecting and converting steps.
 2. The method of claim 1,wherein the graphene nanoribbons are of uniform length
 3. The method ofclaim 2, wherein the uniform length is about 50 μMm, about 100 μm, about150 about 200 μm or about 500 μm.
 4. The method of claim 1, wherein thegraphene nanoribbons are of greater than 90%, 95%, 99%, 99.5% or 99.9%purity.
 5. The method of claim 1, wherein the graphene nanoribbons areof greater than 90%, 95%, 99%, 99.5% or 99.9% purity and is of uniformlength of about 50 μMm, about 100 μm, about 150 about 200 μm or about500 μm.
 6. The method of claim 1, wherein the carbon nanotubes areconverted to graphene nanoribbons by chemical oxidation, plasma etching,electrochemical oxidation or sonochemistry.
 7. A method for synthesizinga mixture of graphene nanoribbons and graphene nanoplatelets comprising:continuously depositing catalyst on a constantly moving substrate;forming carbon nanotubes on the substrate; separating carbon nanotubesfrom the substrate; collecting carbon nanotubes; and converting thecarbon nanotubes to a mixture of graphene nanoribbons and graphenenanoplatelets; wherein the substrate moves sequentially through thedepositing, forming, separating, collecting and converting steps.
 8. Themethod of claim 7, wherein the graphene nanoribbons and graphenenanoplatelets are of greater than 90%, 95%, 99%, 99.5% or 99.9%graphitic carbon purity
 9. A method for synthesizing graphenenanoplatelets comprising: continuously depositing catalyst on aconstantly moving substrate; forming carbon nanotubes on the substrate;separating carbon nanotubes from the substrate; collecting carbonnanotubes; and converting the carbon nanotubes to graphenenanoplatelets; wherein the substrate moves sequentially through thedepositing, forming, separating, collecting, and converting steps. 10.The method of claim 1, wherein the graphene nanoplatelets are of greaterthan 90%, 95%, 99%, 99.5% or 99.9% graphitic carbon purity.